eccentric

You're most likely to encounter the adjective eccentric in a description of an unusual or quirky person — like a scatter-brained aunt who leaves her life savings to her cat.

From the Greek ekkentros, "out of the center," this word originally had to do with the orbits of planets that were observed to be slightly out of whack. Eventually it came to describe people who were a little kooky, both as an adjective and as a noun, too: an eccentric is an unconventional, odd person. Think of them as following a slightly different orbit from the rest of society.